The proposed research aims to examine in detail the genetic consequences of repair of radiation-damaged DNA in the eukaryote Saccharomyces cerevisiae, and the physiology of mutagenesis. The involvement of the products of a number of radiation-sensitive genes in different mutational processes will be examined using the reversion of well-defined cycl alleles to monitor such events, with particular reference to base pair substitution versus frameshift events and the significance of specific nucleotide sequences. Mutations which suppress one or more of the phenotypes of the radiation sensitive mutants will be examined, in order to discover alternate metabolic pathways, and the physiology of mutagenic repair examined by a variety of techniques, including the use of temperature-sensitive mutations. BIBLIOGRAPHIC REFERENCES: C.W. Lawrence and R. Christensen. The influence of the rev2-1 mutations on UV-induced reversion of well defined cycl alleles in the yeast Saccharomyces cerevisiae. Biophysical Journal 16: #2 part 2 (1976). (Abstract). C.W. Lawrence and R. Christensen. UV mutagenesis in radiation-sensitive strains of yeast. Genetics 82:297-332 (1976).